1. Technical Field
The present application relates to a silicon carbide semiconductor device.
2. Description of the Related Art
Silicon carbide (SiC) is a semiconductor material having larger bandgap and higher hardness than those of silicon (Si). SiC is applied to a power element such as a switching element or a rectifier element, for example. The power element using SiC has the advantage of being capable of reducing power loss in comparison with a power element using Si.
A metal-oxide-semiconductor field-effect transistor (MOSFET) is a representative semiconductor element using SiC.
The use of SiC-MOSFET for a switching element used for a power converter for the drive control of a load such as a motor has been considered.
For example, structures described in Patent Literatures 1 and 2 are disclosed as a MOSFET using SiC. In the MOSFET disclosed in PTL 1, an upper source electrode which is electrically connected to respective vertical MOSFET cells is formed on a cell region where a gate pad to which a gate voltage is externally applied and the vertical MOSFET cells are disposed in parallel. Further, a gate line is formed along an outer periphery so as to surround the upper source electrode in a state of being electrically connected to the gate pad. The gate line formed to surround the upper source electrode suppresses a time lag in the potential of the gate electrode according to the distance from the gate pad, thereby increasing the speed of switching. For example, when polysilicon which is not so sufficiently high in conductivity is used for the gate electrode, gate resistance of the MOSFET is increased if the gate electrode is located distant from the gate pad. Therefore, the time lag occurs between the potential of the gate pad and the potential of the gate electrode due to the time constant determined by the gate resistance of the MOSFET and the capacitance between the source and the gate in the MOSFET cell having high gate resistance. In view of this, the gate line is formed from a low-resistance material such as aluminum and formed to surround the upper source electrode, whereby the gate resistance of each MOSFET cell is reduced and a potential is easily supplied to the gate electrode, which increases the speed of switching.
Further, a termination structure is formed at the outside of the gate line. The termination structure has a function of relaxing an electric field on the surface. A junction termination extension (hereinafter abbreviated to JTE) structure or mesa structure in addition to a field limiting ring (hereinafter abbreviated to FLR) structure have widely been used for the termination structure.